1. Field of the Invention
The present invention relates to a resin binder for a toner used for developing electrostatic latent images formed in electrophotography, electrostatic recording method, electrostatic printing, and the like, preferably a toner for electrophotography, and a toner comprising the resin binder.
2. Discussion of the Related Art
Conventionally, as resin binders for a toner which are excellent in various properties required for copy machines, especially excellent in the low-temperature fixing ability and the offset resistance, there have been known a resin binder prepared by mixing a nonlinear high-softening point resin and a nonlinear low-softening point resin (Japanese Patent Laid-Open Nos. Sho 63-225246, Sho 63-225245, Sho 63-225244, 2000-356865, and the like); a resin binder prepared by mixing a nonlinear high-softening point resin and a linear low-softening point resin (Japanese Patent Laid-Open Nos. Sho 60-214368, Hei 4-362956, 2000-39738, Hei 12-39738, and the like); and the like. However, in the former resin binder, since a nonlinear resin is used as a low-softening point resin, the glass transition point is lowered, so that its storage property is unsatisfactory. In the latter resin, specifying the raw material monomers is insufficient, and the storage property, the pulverizability, and the offset resistance are unsatisfactory.
Further, recently, since network printing has become the main trend for copy machines and printers, further improvement has been desired such as suppression of toner odor to make it environment-friendly upon use in addition to the conventionally required properties such as toner performance and production efficiency during its use in a business office.
An object of the present invention is to provide a resin binder which is excellent in fixing ability, offset resistance, storage property and pulverizability and generates little odor even when used as a resin binder for a toner, and a toner comprising the resin binder.
These and other objects of the present invention will be apparent from the following description.
According to the present invention, there are provided:
(1) a resin binder comprising a nonlinear polyester having a softening point of from 130xc2x0 to 160xc2x0 C. and a linear polyester having a softening point of from 80xc2x0 to 110xc2x0 C., wherein the nonlinear polyester is obtained by polycondensing an alcohol component and a carboxylic acid component, wherein
1) an aliphatic dicarboxylic acid compound is contained in an amount of 60% by mol or more of the carboxylic acid component;
2) (i) no alkenylsuccinic acid compound is contained, or
xe2x80x83(ii) if any, an alkenylsuccinic acid compound is contained in an amount of 0.1% by mol or less of the carboxylic acid component; and
3) at least one component selected from the group consisting of:
xe2x80x83(i) a trihydric or higher polyhydric alcohol in an amount of from 0.1 to 40% by mol of the alcohol component; and
xe2x80x83(ii) a tricarboxylic or higher polycarboxylic acid compound in an amount of from 0.1 to 40% by mol of the carboxylic acid component
xe2x80x83is contained, and
wherein the linear polyester is obtained by polycondensing an alcohol component and a carboxylic acid component, wherein
1) an aromatic dicarboxylic acid compound is contained in an amount of 90% by mol or more of the carboxylic acid component; and
2) at least one component selected from the group consisting of (a) and (b):
(a)
xe2x80x83(i) no trihydric or higher polyhydric alcohol, or
(ii) if any, a trihydric or higher polyhydric alcohol is contained in an amount of less than 0.05% by mol of the alcohol component; and
(b) (i) no tricarboxylic or higher polycarboxylic acid compound, or
xe2x80x83(ii) if any, a tricarboxylic or higher polycarboxylic acid compound in an amount of less than 0.05% by mol of the carboxylic acid component
xe2x80x83is contained; and
(2) a toner comprising the resin binder of item (1) above.
The resin binder of the present invention comprises a nonlinear polyester having a high softening point and a linear polyester having a low softening point. In the present invention, by specifying each of raw material monomers for the nonlinear polyester having a high softening point and the linear polyester having a low softening point, there can be obtained a resin binder for a toner which is not only excellent in fixing ability, offset resistance, storage property and pulverizability but also generates little odor upon heating, thereby making the toner environmental-friendly.
Specifically, the nonlinear polyester is obtained by polycondensing an alcohol component and a carboxylic acid component, wherein
1) an aliphatic dicarboxylic acid compound is contained in an amount of 60% by mol or more of the carboxylic acid component;
2) (i) no alkenylsuccinic acid compound is contained, or
(ii) if any, an alkenylsuccinic acid compound is contained in an amount of 0.1% by mol or less of the carboxylic acid component; and
3) at least one component selected from the group consisting of:
xe2x80x83(i) a trihydric or higher polyhydric alcohol in an amount of from 0.1 to 40% by mol of the alcohol component; and
xe2x80x83(ii) a tricarboxylic or higher polycarboxylic acid compound in an amount of from 0.1 to 40% by mol of the carboxylic acid component
xe2x80x83is contained.
The polyester obtained from an aliphatic dicarboxylic acid compound as a raw material monomer has a higher molecular weight at the same softening point, as compared to the polyester using the aromatic compound. Therefore, despite the low lowest fixing temperature, the polyester is effective in improvement of the offset resistance, so that its performance can be sufficiently exhibited by using the polyester as a main component for the high-softening point polyester.
The aliphatic dicarboxylic acid compound includes oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, adipic acid, acid anhydrides thereof, C1-3 alkyl esters of these acids, and the like. The aliphatic dicarboxylic acid compound has preferably from 2 to 10 carbon atoms, more preferably 4 to 6 carbon atoms. Incidentally, as described above, the aliphatic dicarboxylic acid compound refers to aliphatic dicarboxylic acids, acid anhydrides thereof and C1-3 alkyl esters of these acids, among which aliphatic dicarboxylic acids are preferable.
It is desirable that the aliphatic dicarboxylic acid compound is contained in the carboxylic acid component in an amount of 60% by mol or more, preferably from 60 to 99.9% by mol, more preferably from 65 to 90% by mol.
However, a substituted succinic acid of which substituent is an alkenyl group having 2 to 20 carbon atoms, such as dodecenylsuccinic acid and isooctenylsuccinic acid, generates irritable odor upon heat-fixing. Therefore, the content of the substituted succinic acid is preferably as low as possible. Accordingly, no alkenylsuccinic acid compound is contained, or if any, its content in the carboxylic acid component is in an amount of 0.1% by mol or less, preferably 0.05% by mol or less. It is preferable that no alkenylsuccinic acid compound is contained.
As other dicarboxylic acid component, there may be used aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid, acid anhydrides thereof, C1-3 alkyl esters of these acids, and the like.
Further, in order to form a nonlinear structure and improve offset resistance or the like, there are used trivalent or higher polyvalent monomers, namely trihydric or higher polyhydric alcohol and/or tricarboxylic or higher polycarboxylic acid compound. As the trivalent or higher polyvalent monomers, the tricarboxylic or higher polycarboxylic acid compound is preferable, from the viewpoint of improvement efficiency of the offset resistance.
The tricarboxylic or higher polycarboxylic acid compound includes, for instance, 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, pyromellitic acid, acid anhydrides thereof, lower C1-3 alkyl esters of these acids, and the like.
The trihydric or higher polyhydric alcohol component includes, for instance, sorbitol, pentaerythritol, glycerol, trimethylolpropane, and the like.
Each of the content of the trihydric or higher polyhydric alcohol component in the alcohol component and/or the content of the tricarboxylic or higher polycarboxylic acid compound in the carboxylic acid component is from 0.1 to 40% by mol, preferably from 5 to 35% by mol, more preferably from 15 to 30% by mol.
In addition, the dihydric alcohol component includes a compound represented by the formula (I): 
wherein R is an alkylene group having 2 or 3 carbon atoms; each of x and y is a positive number, wherein a sum of x and y is from 1 to 16, preferably from 1.5 to 5.0, including, for instance, an alkylene(2 to 3 carbon atoms) oxide(average number of moles: 1 to 16) adduct of bisphenol A such as polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane and polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl)propane, and the like; ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, neopentyl glycol, polyethylene glycol, polypropylene glycol, bisphenol A, hydrogenated bisphenol A, and the like.
In any of the nonlinear polyester and the linear polyester described below, the main component of the alcohol component is preferably the compound represented by the formula (I), from the viewpoints of storage property and low-temperature fixing ability, of which content in the alcohol component is preferably 50% by mol or more, more preferably from 70 to 100% by mol, still more preferably 100% by mol.
The linear polyester is obtained by polycondensing an alcohol component and a carboxylic acid component, wherein
1) an aromatic dicarboxylic acid compound is contained in an amount of 90% by mol or more of the carboxylic acid component; and
2) at least one component selected from the group consisting of (a) and (b):
(a) (i) no trihydric or higher polyhydric alcohol, or
xe2x80x83(ii) if any, a trihydric or higher polyhydric alcohol is contained in an amount of less than 0.05% by mol of the alcohol component; and
(b) (i) no tricarboxylic or higher polycarboxylic acid compound, or
xe2x80x83(ii) if any, a tricarboxylic or higher polycarboxylic acid compound in an amount of less than 0.05% by mol of the carboxylic acid component
xe2x80x83is contained.
The polyester obtained from an aromatic dicarboxylic acid compound as a raw material monomer has a lower molecular weight at the same softening point, as compared to the polyester using the aliphatic carboxylic compound. The polyester is excellent in the pulverizability, and also excellent in the storage property because of its high glass transition point, so that its performance can be sufficiently exhibited by using the polyester as a main component for the low-softening point polyester.
The aromatic dicarboxylic acid compound includes phthalic acid, isophthalic acid, and terephthalic acid, acid anhydrides thereof, C1-3 alkyl esters of these acids, and the like. Incidentally, as described above, the aromatic dicarboxylic acid compound refers to aromatic dicarboxylic acids, acid anhydrides thereof and C1-3 alkyl esters of these acids, among which aromatic dicarboxylic acids are preferable.
The content of the aromatic dicarboxylic acid compound in the carboxylic acid component is 90% by mol or more, preferably from 95 to 100% by mol, more preferably 100% by mol.
As other dicarboxylic acid component, there may be used the aliphatic dicarboxylic acid compounds mentioned above, and the like.
In the linear polyester, it is also preferable that the content of the alkenylsuccinic acid compound is as low as possible. Therefore, no alkenylsuccinic acid compound is contained, or if any, its content in the carboxylic acid component is in an amount of preferably 0.1% by mol or less, more preferably 0.05% by mol or less.
In addition, in order to form a linear structure, it is preferable that the content of the trivalent or higher polyvalent monomers is low as possible. No trihydric or higher polyhydric alcohol component or no tricarboxylic or higher polycarboxylic acid is contained, or if any, each content of the trihydric or higher polyhydric alcohol component in the alcohol component and/or the tricarboxylic or higher polycarboxylic acid compound in the carboxylic acid component is less than 0.05% by mol.
As the dihydric alcohol component, there may be exemplified the same alcohols as those for the nonlinear polyester mentioned above.
The polyester, regardless of being nonlinear or linear, can be prepared by the polycondensation of the alcohol component with the carboxylic acid component, and the like at a temperature of from 180xc2x0 to 250xc2x0 C. in an inert gas atmosphere, using an esterification catalyst as occasion demands.
In the present invention, since a specified high-softening point polyester and a specified low-softening point polyester are used in combination, the offset resistance is improved due to the high-softening point polyester and the pulverizability, the storage property and the fixing ability are respectively improved due to the low-softening point polyester, so that excellent synergistic effects which are not obtained by a single resin are exhibited.
Therefore, the nonlinear polyester has a softening point of from 130xc2x0 to 160xc2x0 C., preferably from 140xc2x0 to 160xc2x0 C., more preferably from 140xc2x0 to 150xc2x0 C., from the viewpoints of the offset resistance and the pulverizability, and the linear polyester has a softening point of from 80xc2x0 to 110xc2x0 C., preferably from 85xc2x0 to 107xc2x0 C., more preferably from 90xc2x0 to 105xc2x0 C., from the viewpoints of the fixing ability and the storage property.
The weight ratio of the nonlinear polyester to the linear polyester in the resin binder of the present invention, i.e. nonlinear polyester/linear polyester, preferably from 90/10 to 20/80, more preferably from 80/20 to 30/70, especially preferably from 75/25 to 40/60.
The toner of the present invention may contain, in addition to the resin binder of the present invention, a styrene-acrylic resin, a composite resin of a polyester and a styrene-acrylic resin, an epoxy resin, a urethane resin or the like, in an amount so as not to impair the effects of the present invention. Further, the toner may appropriately contain an additive such as a colorant, a charge control agent, a releasing agent, a fluidity improver, an electric conductivity modifier, an extender, a reinforcing filler such as a fibrous substance, an antioxidant, an anti-aging agent, or a cleanability improver.
As the colorant, all of the dyes and pigments which are used as colorants for a toner can be used, and the colorant includes carbon blacks, Phthalocyanine Blue, Permanent Brown FG, Brilliant Fast Scarlet, Pigment Green B, Rhodamine-B Base, Solvent Red 49, Solvent Red 146, Solvent Blue 35, quinacridone, carmine 6B, disazoyellow and the like. These colorants can be used alone or in admixture of two or more kinds. The toner of the present invention can be used as any of black toners, monochromatic toners, and full color toners. The content of the colorant is preferably from 1 to 40 parts by weight, more preferably from 3 to 10 parts by weight, based on 100 parts by weight of the resin binder.
The process for preparing a toner of the present invention may be any of known methods such as a kneading-pulverization method, a polymerization method, a phase-inversion method or the like. In a case where the toner is a pulverized toner prepared by a kneading-pulverization method, for instance, the toner is prepared by the step comprising homogeneously pre-mixing a resin binder, a colorant or the like in a mixer such as a Henschel mixer or a ball-mill, thereafter melt-kneading the mixture with a closed kneader, a single-screw or twin-screw extruder, or the like, cooling, pulverizing and classifying the product. The volume-average particle size of the toner thus obtained is preferably from 3 to 15 xcexcm. Further, a fluidity improver or the like such as hydrophobic silica may be added to the surface of the toner.
The toner of the present invention is used alone as a developer, in a case where the fine magnetic material powder is contained. Alternatively, in a case where the fine magnetic material powder is not contained, the toner may be used as a nonmagnetic monocomponent developer, or the toner can be mixed with a carrier and used as a two-component developer.